The term “tramp metal” is used to refer to any metal which is present with a material being processed, which should not be present. It can enter the material stream with the material from an outside source or come from components of the machinery carrying out the procedure.
The presence of tramp metal in materials being processed can cause problems both to the composition of the processed material and to equipment being used in the processing. Therefore, it is known to provide tramp metal detectors at one or more locations along a processing line to detect any tramp metal, in order that action can be taken to remove it from the material stream. A convenient location for installing a tramp metal detector is along a conveying machine, for example a conveying belt, on which the material being processed is loaded.
For materials being processed, which are non-metallic, a metal detector utilizing a magnetic field is typically provided. The material being processed passes through the magnetic field and any disturbance to the field can be detected. Non-metallic material passing through the field may result in a slight disturbance of the field, however, if tramp metal or the like passes through the field a significant and detectable disturbance should result. However, in order for the detecting system to be reliable and in order that nuisance false detections do no occur, it is necessary to maintain the detecting equipment in a well calibrated state.
Processing equipment on which the present invention is beneficial is often located outdoors, is subject to the elements and is often subject to dust, heat etc. which often makes maintaining the calibrated state difficult. Calibration of the equipment may have to be carried out frequently in order to enable safe and efficient operation of the processing line.
Detecting equipment, as described above, is most accurately calibrated by inserting at least one sample, which is representative of metal most likely to be detected, into the magnetic field at a location at which tramp metal would most likely pass if contained in the material being processed. Therefore, calibrating is best performed by discontinuing loading of material on the belt, in order that the pertinent area in the magnetic field is free of the material being processed. This procedure is preferred in order that the sample material of the calibrating device can be placed in the best location for calibrating. Since a discontinuation in loading results in a decrease in production, it is desirable to carry out the calibrating operation in as short a time as possible, but without sacrificing accuracy.
Therefore, there is a need for a device and a method for quickly and accurately calibrating a tramp metal detector on a materials processing line.